1. Field of the Invention
The present invention relates to an optical recording method on a multilayer optical recording medium having a plurality of recording layers, an optical recording apparatus adopting the recording method, and a multilayer optical recording medium.
2. Description of the Related Art
When information is recorded by irradiating a recording layer of an optical recording medium with a beam spot of a laser or the like, various factors can cause a recording error. Some of the factors that can cause a recording error include the meandering of a recording track on the optical recording medium, bumps and dips in the recording track, air bubbles in a spacer layer, and the like. Other factors causing a recording error may also include foreign matter such as a fingerprint, dust, and the like adhering to the surface of the optical recording medium.
In order to appropriately avoid a defect area in which any such factor exists, a recording technology has been developed which checks for a defect prior to the recording of data. For example, there is a method for detecting a defect (dropout) which utilizes the reflected light of the beam spot when recording information. Use of the reflected light of the beam spot when recording can allow for the detection of a tracking error, a focus error, and the like, so that any defect in the recording layer can be determined by the extent of these errors. When it is determined that a dropout has occurred, an optical pickup is shifted in a radial direction in order to avoid the recording track that has the defect and information is then recorded on a different recording track. Using an alternative area like this makes it possible to avoid the defect area. In order to detect the defect area, an inspection method that irradiates the recording track with a beam spot before recording is used. When information is recorded on the alternative area, being a different recording track, thereby avoiding the defect area, translation table information which contrasts the sector address of the defect area with the sector address of the alternative area is recorded on a defect management area provided at the innermost or outermost circumference of the optical recording medium. When the information is reproduced the next time, reference to the defect management area in order to obtain a translation table makes it possible to smoothly reproduce the information.
In recent years, a multilayer optical recording medium having a plurality of recording layers has been proposed as the preferred optical recording medium. A specific recording layer is irradiated with a beam spot by controlling the focus of a laser beam, so that information is recorded on each recording layer. Presently, if a defect area exists in each recording layer, the beam spot moves in a radial direction and records information on a different recording track in the same recording layer. A defect management area is formed at the inner or outer circumference of each recording layer. When the operation to avoid the defect area (hereinafter referred to as the escape operation) is carried out, a translation table and the like are recorded on the defect management area of that recording layer.
In this kind of multilayer optical recording medium, since the defect management area can be allocated in each recording layer, it is proposed that the translation table of the specific recording layer is concurrently recorded on the defect management area of another recording layer in order to duplicate the translation table (see Japanese Patent Application Laid-Open No. 2001-014808).
In the multilayer optical recording medium, when the defect management area is secured in the innermost or outermost circumference of each recording layer, all defect management areas are overlapped in the data stacking direction. Thus, when the innermost or outermost circumference is scratched, all the defect management areas become unavailable at the same time. In order to resolve this problem, a method for dispersively disposing the defect management areas so as not to overlap in the data stacking direction among a plurality of recording layers in a multilayer optical recording medium has been proposed (Japanese Patent Application Laid-Open No. 2006-500713).
In both Japanese Patent Application Laid-Open Nos. 2001-014808 and 2006-500713, however, in order to avoid the defect area, it is necessary to shift the optical pickup in the recording layer in the radial direction. Thus, in the case of a recording method in which the number of revolutions of a motor varies in accordance with the radial position of the optical pickup, like zone CLV, there is a problem in that control over the number of revolutions of the optical recording medium takes time and hence the recording rate is reduced during the escape operation.
The radial shift distance of the optical pickup in the escape operation is set to be sufficiently large so as to ensure escape from the defect area. As a result of this, there is a problem in that the storage capacity of the recording layer in which the defect area is detected is reduced. It is conceivable that information is separately recorded on an allowance sector between the defect area and an escape area. In such a case, however, there is a problem in that readout efficiency is reduced because the information is recorded on radially dispersive recording areas in fragments.
Furthermore, when the shift mechanism of the optical pickup used in the conventional recording method is broken and the optical pickup cannot be shifted in the radial direction, there is a problem in that it is impossible to safely end the information recording operation because the escape operation cannot be carried out.
At present, conventional optical recording media have the problem of being unable to achieve nominal storage capacity if a defect area occurs. In particular, if the entire storage capacity is increased due to a multilayer structure, the capacity is extensively varied in accordance with the rate of defect areas, so that there is conceivably a case where a user expecting the nominal storage capacity printed on a package will find it to not actually be achievable.